System for controlling the steering of vehicle wheels

ABSTRACT

In a steering control system for vehicle wheels in which rotational axis of the wheels are disposed in a plane at the vertices of a polygon which can be inscribed within a circle referred to as a base circle, the direction of the axes of rotation of the wheels is caused to converge continuously towards a common point referred to as the center of rotation of the vehicle and the circle which circumscribes the base polygon in the base plane corresponds by means of a geometrical transformation to a reference circle in a reference plane, said center of rotation being related alternately its transformed point in said reference plane and to the harmonic conjugate of said point with respect to said reference circle.

United States Patent [72] Inventors Jean-pierre Guilbaud JouarsPonchartrain; Jean Vertut, Paris, France [2]] Appl. No, 812,037 [22]Filed Apr. 1, 1969 [45] Patented May 11, 1971 [73] Assignee CommissariatA LEnergie Atomique Paris, France [32] Priority Apr. 9, 1968 [33] France[3 l 147,453

[54] SYSTEM FOR CONTROLLING THE STEERING OF Primary Examinerl(enneth H.Betts Assistant Examiner.lohn A. Pekar Attorney-Cameron, Kerkam & SuttonABSTRACT: In a steering control system for vehicle wheels in whichrotational axis of the wheels are disposed in a plane at the vertices ofa polygon which can be inscribed within a circle referred to as a basecircle, the direction of the axes of rotation of the wheels is caused toconverge continuously towards a common point referred to as the centerof rotation of the vehicle and the circle which circumscribes the basepolygon in the base plane corresponds by means of a geometricaltransformation to a reference circle in a reference plane, said centerof rotation being related alternately its transformed point in saidreference plane and to the harmonic conjugate of said point with respectto said reference circle.

PATENTED um I l97l saw 3 OF 6 PATENTEDHAH 1 I97! 3578'097 sum u or 6SYSTEM FOR CONTROLLING THE STEERING OF VEHICLE WHEELS This invention isconcerned with improvements to systems for controlling the steering ofthe wheels of a vehicle, whereby the wheel-turning radius can be variedbetween a value at which the center of rotation is projected to infinityin the case in which the wheels are parallel and a zero value at whichthe center ofrotation is located at the center of the vehicle whichaccordingly rotates about this point. A further aim of the invention isto permit the displacement of the center of rotation in the plane whichpasses through the axes of rotation of all the wheels irrespective ofthe value of the turning radius, thereby endowing the vehicle with themost general plane on plane motion.

Steering control systems which are already known suffer from a firstlimitation in that the center of rotation must necessarily remain on astraight line which is related to the vehicle and usually materializedby the rear axle centerline located at right angles to the longitudinalaxis of the vehicle. In the simplest case of a three-wheeled vehicle inwhich a single wheel has both a driving and steering function and inwhich the axis of pivotal motion of the wheel is located in the plane atright angles to the commondirection of the axle of the other two wheels,it is possible to displace the center of rotation to any point of thestraight line of the rear axle; however, a vehicle of this typeevidently lacks stability and is suitable only for limited applications.In the derived casein which the wheels of a vehicle are disposed in alozenge configuration corresponding to the juxtaposed assembly of twothree-wheeled vehicles on a common axis, the degree of stabilityachieved is still not perfect. ln addition, only two wheels can haveboth a driving and a steering function at the same time.

ln the most common case of four-wheeled vehicles, a further limitationhas to be taken into consideration, namely the fact that the center ofrotation can be displaced along the straight line of the rear axle onlybetween given limits. In fact, the front wheels are usually mounted onkingpins which define their respective pivotal axes and are controlledby steering tie rods, the compensated displacements of which are relatedto the operation of the steering wheel by means of a toothed rack.During this pivotal motion of the wheels, the center of rotation isdisplaced between infinity, in which case all wheels are parallel, andan ultimate or limiting point which is close to the vehicle but locatedoutside the rectangle of the four wheels; this limiting point definesthe minimum turning radius.

The aim of the present invention is to provide a remedy for thesedisadvantages by permitting any desired displacement of the center ofrotation in the plane which contains the axes of rotation of all thewheels and any desired number of wheels. Moreover, all the wheels can beendowed either simultaneously or separately with either a driving orsteering function or both at the same time. The invention appliesgenerally to a vehicle in which the pivot axes of the wheels intersect abase plane at the vertices of a base polygon which can be inscribed in abase circle. As a preferable feature, the plane of the base polygon isperpendicular to the pivotal axes of said wheels which are all parallel.However, the invention would also be applicable to the case in which thepivotal axes of the wheels are not necessarily normal to the plane ofthe base polygon; these wheels can also have particular angles ofinclination to this plane, as is the case with conventional motorvehicles in which the support polygon defined by the points of contactof the wheels with the ground is not directly similar to the base plygon and is not deduced from this latter simply by orthogonalprojection on the plane of the ground.

To this end, the system under consideration is characterized in that,inasmuch as the direction of the axes of rotation of the wheels iscaused to converge continuously towards a common point known as thecenter of rotation of the vehicle, the circle which circumscribes thebase polygon in the base plane corresponds by means of a geometricaltransformation to a reference circle in a reference plane, said centerof rotation being related alternately to its transformed point in saidreference plane and to the harmonic conjugate of said point with respectto said reference circle.

, Preferably, said geometrical transformation is a similitude whichconstitutes a translation in an extreme case.

In a simplified embodiment of the invention, said transformed point iscaused either mechanically or electrically to carry out a displacementalong a straight line of the reference plane. In a more generalarrangement, said straight line is capable of carrying out a pivotalmotion about a point in said reference plane, the combination of thedisplacement of said point on said straight line andthe pivotal motionof this latter being such that said point is permitted to take up anyposition in said plane.

By virtue of the foregoing arrangements, two possible positions of thecenter of rotation correspond to each position of the transformed pointin the reference plane within the reference circle. The first possibleposition in which the transformed point is directly related to thecenter of rotation places this latter inside the base circle which isdeduced from the reference circle as a result of the reversetransformation; the second possible position in which the harmonicconjugate of the transformed point which is related to the center ofrotation conversely places said center outside the base circle. Thecenter of rotation can thus take up any position either inside oroutside said circle corresponding to the homologous, continuous andunlimited displacements of the transformed point within the referencecircle.

in a first mode of execution of the invention, the position of thetransformed point with respect to the reference circle is determined bymeans of forks which are pivotally mounted at the vertices of thereference polygon and the ends of which are adapted to cooperate with acontrol pin, said pin being operated within a guide slot whichmaterializes a straight line of the reference plane. In accordance withthe invention, the angular displacements of the forks determine in thecase of the vehicle wheels which are associated with the vertices of thebase polygon either equal or opposite displacements according as thecenter of rotation is located either inside or outside the base circle.

To this end, said system is essentially characterized in that itcomprises a control plate in which is formed a guide slot, a first setof forks which are capable of being directly keyed on the pivotal shaftsof the wheels and extend parallel to the plane of said control plate soas to come into engagement with a first pin which is engaged in saidslot, first pinions which are rigidly fixed to said pivotal shafts anddisposed in meshing relation with second pinions having the samediameter which are carried by swivel pins located parallel to thepivotal shafts and fixed on said control plate, a second set of forkswhich are capable of being directly keyed on said swivel-pins and extendparallel to the plane of said control plate so as to come intoengagement with a second pin engaged in a second slot of said controlplate, the centers of the second pinions being located on the referencecircle of which the second slot constitutes a diameter, said referencecircle being deduced by translation of the base circle in the directionwhich joins the pivotal shafts to the associated swivel-pins and theamplitude of which is equal to the common diameter of the first andsecond pinions. Preferably, said direction is parallel to the first slotwhilst the second slot coincides with the first. As a further preferredfeature, the forks of the first and second sets are parallel anddisposed respectively on each side of the faces of said control plate.

In another embodiment of the invention, said first and second pinionsare capable of being alternately coupled to the pivotal shafts of thewheels by means of keys slidably fitted on said shafts, each pair ofpinions having the same diameter being coupled together by means of aplanetary pinion whose diameter defines the amplitude of the translationwhich causes the base circle to correspond to the reference circle, saidpivotal shafts being additionally coupled with a set of third identicalpinions which are in meshing relation by means of bevel pinions with afourth or common pinion which is carried by'a shaft located parallel tothe pivotal shafts and which is adapted to support the guide slot forthe control pins, the diameter of said fourth pinion being equal to thediameter of the bevel pinions and one-half the diameter of the thirdpinions.

Finally, in another embodiment, said control plate comprises a referencecircle which is deduced from the base circle by virtue of a similitudeand a set of circular electric potentiometers disposed on said circle atthe vertices of the reference polygon and having sliding contacts whichare caused to converge towards a common pin constituting the transformedpoint of the center of rotation, said pin being capable of displacementalong a diameter of said reference circle and the pivotal shafts of thewheels being driven by individual motors supplied as a function of thepositions of the sliding contacts of the duplicating potentiometerswhich are each associated with a corresponding potentiometer of saidcontrol plate. In addition, said control plate is provided at theextremities of the diameter of the reference circle on which saidcontrol pin is capable of displacement with relays for reversing thedirections of polarity of the duplicating potentiometers which controlthe individual motors of the pivotal shafts so as to ensurecorrespondence between said center of rotation and its transformed pointor its harmonic conjugate relative to said reference circle.

The different properties mentioned in the foregoing and consideredseparately or even in combination will be explained in greater detail inthe following description of a number of practical examplescorresponding to the different modes of execution set forth hereinabove.It will be readily understood that said examples are given solely by wayof indication and not in any limiting sense and that any alternativeforms which utilize the same properties must be considered as remainingwithin the scope of the present invention.

In the accompanying drawings:

FIG. 1 is a diagrammatic view of a portion of a vehicle which isequipped with a steering control system in accordance with theinvention;

FIGS. 2 and 3 are diagrams relating to the embodiment of FIG. 1 andserving to explain its operation;

FIG. 4 is a perspective view of an embodiment which is derived from thatof FIG. 1;

FIG. 5 is another perspective view of another embodiment of more highlyimproved design;

FIG. 6. is an explanatory diagram of the embodiment of FIG.

FIG. 7 illustrates another alternative embodiment;

FIGS. 8 and 9 are explanatory diagrams of operation of the alternativeembodiment shown in FIG. 7.

There is shown diagrammatically in FIG. I a vehicle 1 comprising only apart of the steering control system as constructed in accordance withthe invention and serving to gain a clearer conception of its generalstructure as shown by way of example in the perspective view of FIG. 4.

The vehicle 1 shown in FIG. 1 has a frame 2 in the form of a flat plateon which are mounted a series of pivots 3 each associated with a wheel 4by means of a stub axle or axle-pin S. Said pivots 3 are in parallelrelation and oriented at right angles to the plane of the plate 2; inthe example under consideration, the pivots are also spaced on a circlewhich defines the base circle mentioned earlier and the extremities ofthe pivots constitute on said circle the vertices of the base polygon.There is mounted at the extremity of each pivot 3 a pinion 6 which issecured to the shaft of the corresponding pivot by suitable means. Saidpinion 6 is adapted to cooperate with a second pinion 7 having the samediameter and mounted at the end of a swivel-pin 8 which is parallel tothe axis of the corresponding pivot. All the pairs of pinions 6,7 whichare associated with the wheels 4 are identical by design, thestraightline segments which join the centers of these pinions beingparallel to each other and having the same length from one pair to thenext. In consequence, the centers of the pinions 7 which correspond tothe swivel-pins 8 are disposed on a circle having the same diameter asthe circle relating to the pinions 6. This second circle or so-calledreference circle isdeduced from the first base circle by means of ageometrical transformation which is in this case a translation in thedirection of said straight-line segments and equal in amplitude to thediameter of any one of said pinions. There is fixed on each pinion 7 afork 9 adapted to engage with a pin 10 which is parallel to the pivots3, said pin 10 being intended to produce the convergence of all theforks which are associated with all the pinions 7. Moreover, said pin 10is caused by any known means to carry out a movement of displacementwithin a slot 11 which is formed in the example illustrated in thedrawings through the thickness of the plate 2. Said slot extends along adiameter of the reference circle which passes through the centers of thepinions 7. The displacements of the pin 10 from one end of the slot 11to the other accordingly make it possible by means of the pinions 6 and7 to control the orientation of the wheels 4 about their respectivepivots 3 and consequently to determine the resultant displacement of thecenter of rotation of the vehicle. In the case which is illustrated inFIG. I, this displacement of the center of rotation is carried out frominfinity when the pin 10 is located at the center of the slot 11, thatis to say at the center of the reference circle up to a point whichforms part of the base circle when the pin 10 is located at either ofthe two ends of said slot 1 I, that is to say when the pin reaches theextremities of the diameter of the reference circle which ismaterialized by said slot.

The operation which is explained in the foregoing will be more readilyunderstood with reference to FIG. 2. There is shown in this FIG. thereference circle 12 which circumscribes the axes of the pinions 7 andthe base circle 13 which circumscribes the axes of the pivots 3, that isto say which passes through the axes of the pinions 6. For the sake ofenchanced clarity, there has been shown in FIG. 2 only a single pair ofpinions 6,7, it being understood that the demonstration givenhereinafter applies at the same time to all the other pairs which, asstated earlier, are disposed on the circles 12 and 13 respectively. Thepoints A and B on the circle 12 delimit a diameter corresponding to theslot 1 l in which is displaced the pin 10, the axis of which isrepresented at C. The point D on the circle 12 represents schematicallythe axis of the pinion 7 as outlined whilst the point E on the circle 13materializes the axis of the associated pinion 6. The circles 12 and 13are deduced from each other by means of a translation which takes placein the direction of the segment DE and the amplitude of which is equalto the length of said segment, that is to say to the diameter of thepinion 6 which is made equal by design to the diameter of the pinion 7.

If, on the line of extension of the diameter AB, the point C designatesthe conjugate of th point C relative to the reference circle 12, theangle being a ri ht angle, the result there achieved is that the angles65% on the one hand and D on the other hand are equal whilst thestraight line DB bisects the angle GDT' in accordance with a knownproperty of harmonic beams. Moreover, the pinion 6 rotates continuouslythrough an angle which is opposite to that which is described by thepinion 7 when this latter is driven about its axis D as a result of themotion of its fork caused by the displacement of the point Crepresenting the control pin 10 within the slot 11. In point of fact,said pinion 6 is coupled by means of its pivot 3 to one of the wheels 4of the vehicle whose rotational axis is defined by the straight line EFwhich is parallel to the straight line DC. The result thereby achievedis that the point F which corresponds to the center of rotation of thevehicle is deduced from the point C' by means of the same translationwhich causes the reference circle I2 to correspond to the base circle13. Under these conditions, when the point C carries out a displacementalong the diameter AB inside the reference circle, the point F isdisplaced along the diameter GH of the base circle but outside thislatter between infinity and the extremities G and H. When F is atinfinity, that is to say when the point C is located at the center ofthe reference circle 12, the corresponding wheel 4 is perpendicular tothe straight line GH. On the other hand, when the point C arrives at B,for example, the point F comes to H at the limits of the diameter GHwhich corresponds to the base circle.

The foregoing demonstration as applied to all the wheels of the vehicletherefore clearly shows that the arrangement contemplated herein carriesout in respect of a displacement of the control pin within its slot 11inside the reference circle a displacement of the center of rotation Fof the vehicle between infinity and the limits of the base circle asdeduced from the reference circle by'meansof a given geometricaltransformation.

Consideration will now be given to an extreme case in which the controlpin 10 reaches the end of its slot 11, that-is to say when, in FIG. 2,the point C reaches one extremity of the diameter of the referencecircle at B, for example. As has already been mentioned, the point Fwhich is the center of rotation of the vehicle and which defines theorientation of the wheels arrives at H, El-l being parallel at thisinstant to DB. Under these conditions, the axis EH of the wheel 4 andthe corresponding fork as materialized by the straight line DB arededuced from each other as a result of the same translation as thatwhich causes the base circle 13 to correspond to the reference circle12. Consequently, if the keying of the wheels is modified in thisposition so that the pinions 7 are freed and rotate freely on theirswivel pins 8 whilst a second set of forks is associated with thepivotal axes of the wheels or in other words with the pivots 3 anddirectly couples said pivots and corresponding pinions 6 to a secondcontrol pin which is capable of displacement within the base circlealong the diameter GH, it is therefore apparent that the vehicles wheelsare directly driven by means of said second control pin by ensuring theconvergence of all the rotational axes towards the center of rotationwhich, in this case, is located inside the base circle 13. The point Fillustrates in FIG. 2 the corresponding position of the center ofrotation.

FIG. 3 illustrates an alternative construction which is derived directlyfrom the construction of HO. 2 in which the translation which causes thebase circle 13 to correspond to the reference circle 12 is carried outin a direction parallel to the diameter AB of the reference circle.Under these conditions, the diameter GH of the base circle coincideswith AB, which means that the slot 11 is common to the two control pinswhich produce the pivotal motion of the wheels according as the centerof rotation is located either inside or outside the base circle or inother words is directly related to its transformed point within thereference circle or to the conjugate of this point with respect to saidcircle.

It should nevertheless be noted that, in these two alternative forms,the geometrical transformation which produces a transition from the basecircle to the reference circle is a translation; it will be apparentthat, generally speaking,

another transformation and especially a similitude could becontemplated.

FIG. 4 illustrates a construction which is directly deduced from thegeneral variant illustrated in FIG. 3. There is again shown in this FIG.a vehicleequipped with a steering control system in accordance with theinvention and comprising any desired number of wheels, the axes of whichare in parallel relation and disposed on a given circle or base circle.There are shown in the drawing only two wheels mounted on axlepins 22carried by bearing-brackets 23 each having a vertical shaft 24 whichconstitutes the pivotal axis of the associated wheel 21 and the angularposition of which is controlled by the system in accordance with theinvention. The pivotal shafts 24 of the wheels are supported by theframe 25 of the vehicle which comprises two parallel and suitably bracedplates 26 and 27. Each pivotal shaft 24 is provided in the portionlocated between said two plates with a member 28 which forms a tenon andhas two flat faces 29 which are oriented parallel to the plane definedby the pivotal shaft 24 and the axle-pin 22 of the corresponding wheel21. At the two portion thereof, the pivotal shaft 24 passes through theplate 27 within the bore of a bushing 30 and terminates in a pinion 31.The

same arrangement as that described above is adopted in the case of allthe other wheels of the vehicle; Swivel-pins 32 which are associatedwith each pivotal shaft 24 and parallel thereto are mounted in the upperplate 27 of the frame 25 and traverse the plate 27 through supportbushings 33. These members are provided at the upper extremities thereofwith pinions 34 disposed in meshing relation with the correspondingpinions 31; the pinions 31 and 34 are of identical diameter in order toproduce in respect of a rotation of one pinion through any given anglein equal rotation of the other pinion but in the opposite direction.Furthermore, each swivel-pin 32 has an extension above the pinion 14 inthe form of a member 35 which forms a tenon, said tenon being similar tothe member 28 and having flat faces 36 oriented in a directionperpendicular to the faces 29 of said member 28. The swivelpins 32 canbe located on the plate 27 in any desired position with respect to thepivotal shafts 24 provided that said position remains the same in eachpair of pinions which are associated with the different wheels 21 of thevehicle. This position is established by design and, in the exampleunder consideration, is parallel to the position of a slot 37 which isformed through the plate 27 and provides a communication between the topand bottom faces of this latter. Provision is made within the slot 37for a rack 38 in meshing engagement with a drive pinion 39 carried by apin 40 which is located at right angles to I the plate 27 and extendsupwards, said pinion 39 being mounted within a support 41 which isguided in its movement of displacement along the slot 37 by means offlanges 42 and 43 formed at each end. ,Moreover, the support 41 isprovided with a second pin 44 which is parallel to the pin 40 butdisplaced with respect to this latter in the direction of the slot 37 bya distance equal to that which exists between the axes of the pinions 31and34 in any given pair, that is to say to the diameter of one of thesepinions. Said second pin 44 extends downwards in the opposite directionto the pin 40.

In accordance with the invention, the system comprises two sets of forkswhich cause the axes of rotation of the wheels to converge towards thecenter of rotation according as this latter is located either inside oroutside the base circle as explained with reference to FlGS. 2 and 3.Depending on whether they are disposed parallel to the plane of theplate 27 within the space formed between said plate and the bottom plate26 or above the plate 27, said forks are designated by the referencenumeral 45 or 46. The forks 45 are provided with internal faces 47 whichare adapted to cooperate with the faces 29 of the member 28 whilst theforks 46 are provided with internal faces 48 which are adapted to guidethe faces 36 of the corresponding members 35. All the lower forks 45 arejoined atone end to the pin 44. Similarly, all the upper forks 46 arecoupled at the common extremity thereof to the pin 40. Finally, theforks 45 on the one hand and 46 on the other hand can be displacedsimultaneously in a vertical movement by means of a clamping bracket 49which is guided along the pins 40 and 44 and is provided with twoshouldered extensions 50 and 51 for lifting the forks under the actionof a tractive force exerted on an operating lever 52.

The operation of the system as thus constructed can readily be deducedfrom the indications which have already been given in the foregoing.When the circle of rotation is to be brought inside the base circle,that is to say the circle which passes through the pivot-pins 24 of thewheels 21, the lower forks 45 accordingly produce action by cooperatingwith the flat faces 29 of the members 28; all the axle-pins 22 convergetowards the pin 44 which materializes the center of rotation in theplane of said axle-pins. In this case, the upper forks 46 are freed fromthe members 35 and do not produce any action on the pinions 34 which areonly caused to follow the angular displacements of the pinions 31. Onthe other hand, when the center of rotation is to be brought outside thebase circle, the operation is as follows: when the support 41 has beenbrought to one of the ends of the slot 37 or in other words to one ofthe extremities of the diameter of the reference circle, the clampingbracket 49 is operated in such a manner as to lower both sets of forksat the same time. The lower forks 45 move away from the members 28whilst the upper forks 46 engage the members 35. When the pin 40 carriedby the support 41 again travels along the slot 37, the angulardisplacements of the pinions 34 are transmitted to the wheels 21 bymeans of the pinions 31, that is to say with reversal of the directionof rota tion. There thus corresponds to each position of the pin 40 oneposition of the center of rotation or point of convergence of theaxle-pins 22 of the wheels 21 which is located outside the base circle.The center of rotation therefore undergoes a displacement which iscontrolled at will over the full length of the straight line representedby the diameter of the reference circle as defined by the slot 37.

FIG. illustrates a more highly improved alternative form of the steeringcontrol system according to the invention whereby, in addition to adisplacement 'of the transformed point of the center of rotation or ofits harmonic conjugate within a slot extending along a diameter of thereference circle, said slot can be pivoted in its plane so that thetransformed point can thus be moved to any desired position within saidcircle.

There is again shown in this FlG. a vehicle which is equipped with agiven number of wheels 61, each wheel being mounted on an axle-pin 62supported by a bracket 63 secured to a shaft 64 which constitutes thepivotal axis of the wheel considered. By definition, all the pivotalshafts 64 of the wheels 61 are parallel and disposed in a circle whichdefines the base circle of the vehicle. Said pivotal shafts 64 aremounted in a frame 65 made up of two parallel spaced plates 66 and 67which are suitably braced. In the portion located between the two plates66 and 67, each pivotal shaft 64 is as sociated with two identical bevelpinions 68 and 69 which are mounted on said shaft and capable of beingalternately coupled for rotation with this latter by means of adog-coupling ring 70 which is slidably mounted but rotationally keyed onthe shaft 64. Said sliding ring is provided with projections or dogs 71which are adapted to engage in recesses having corresponding dimensionsand formed in the opposite faces of the pinions 68 and 69. Positioningof the dog-coupling ring 70 along the shaft 64 in order to couple saidring to either of the two pinions considered is controlled by means of akey 73 provided with a lug 74 which is adapted to engage in a groove 75of the dog-coupling ring 70. Said key has an extension in the form of ahandle 76 so that, in certain positions of the pinions which will bedefined below, the dogs 71 or 72 of said coupling ring aie permitted toengage in their respective recesses of the pinions 68 or 69. Each pinion69 is rigidly fixed at its upper extremity by means of a nut 77 to afork-shaped member 78 having a U-shaped transverse cross section and theupper arm 79 of which is provided with a longitudinal slot 80. All theforks 78 which are thus associated by means of the pinion 68 or 69 whichthe pivotal shafts 64 corresponding to the different wheels of thevehicle are connected at a common point materialized by a control pin 81which is normal to the plane of the top plate 67 of the frame 65. Saidcontrol pin 81 is mounted in a support 82 and provided at the lower endwith a pinion 83 disposed in meshing relation with a rack 84 machined ina diametral slot 85 of a rotary disc 86 which is disposed parallel tothe plane of the plate 67 and engaged within the interior of the U ofall the forks 78. The rotary disc 86 is provided in the outer surfacethereof with gear-teeth 87 meshing with an outer pinion 88 carried by amember 89 which is rigidly fixed to the frame 65 and provided with adriving pin 90 for causing the rotary disc to carry out a pivotal motionabout its shaft 91. The disc shaft extends substantially to the centerof the frame 65 at right angles to the plane of the plates 66 and 67 andis provided at the lower end with a spurtooth pinion 92. Said pinion 92is in mesh with a set of identical pinions 93 having the same diameteras the pinion 92 and mounted to rotate freely on shafts (not shown inthe drawings) which are carried by the plate 66 and are equal in numberto the pivotal shafts 64 and consequently to the wheels 61. Each pinion93 is in turn adapted to mesh with a pinion 94 which is coupled forrotation with the pivotal shaft 64 of the corresponding wheel, thediameter of said pinion 94 beingdouble that of the pinion 92. Finally,each pinion 94 is rigidly fixed to a bracket 95 which is adapted tocarry a differential planetary pinion 96. Said planetary pinion ismounted to rotate freely on its shaft and adapted to engagesimultaneously with both of the pinions 68 and 69 which are associatedwith the corresponding pivotal shaft 64. Advantageously, the key 73which controls the position of the dog-coupling ring 70 on the pivotalshaft 64 passes axially through the planetary pinion 96.

The operation of the system which is illustrated in FIG. 5 can bedirectly deduced from the operation which was explained earlier withreference to FIGS. 1 to 4. The operation involves two main steps,depending on whether the center of rotation of the vehicle is to bebrought either inside or outside the base circle. in the structure whichis illustrated in this FIG, it is observed that the reference circlewhich is materialized by the axes of the pinions 69 is deduced directlyfrom the base circle materialized by the pinions 68 by means of a simpletranslation parallel to the common direction of the pivotal shafts 64,these two circles being therefore equal by design.

In the first step in which the center of rotation of the vehicle isintended to be located inside the base circle, the dogcoupling rings 70are in the top position on their shafts 64, the dogs 72 of said ringsbeing engaged in the corresponding recesses of the pinions 69. Underthese conditions, the shafts 64 are coupled for rotation with saidpinions 69 and these latter are in turn driven directly by the forks 78which converge towards the control pin 81. At each moment, the directionof any axle-pin 62 of a wheel 61 is therefore parallel to that of thecorresponding fork 78*; the center of rotation thus coincides on theshaft 91 with its transformed point in the translation which causes thebase circle to correspond to the reference circle. As in the exampledescribed earlier, the displacement of the control pin 81 within theslot by means of the pinion 83 and the rack 84 determines under theseconditions the displacement of the center of rotation along a diameterof the base circle.

1n the second step, when the center of rotation is intended tocorrespond not to its transformed point in the reference circle but tothe harmonic conjugate of said point relative to said circle, the systemis controlled in the following manner: in the case of a limiting pointof the operation in the first step, that is to say when the control pin81 is located at one extremity of the diameter'of the reference circledefined by the slot 85, the keys 76 are operated so as to ensurethat-the dog-coupling rings 70 are released from the pinions 69 andcoupled to the pinions 68 by means of their projections .or dogs 71which are. accordingly designed to be located opposite to thecorresponding recesses. Under these conditions, the pinions 69 arereleased on the shafts 64 whilst these latter are accordingly coupledfor rotation with the pinions 68. In consequence, the pivotal shafts 64carry out an equal angular displacement but in the opposite direction tothat of the pinions 69 which corresponds to a displacement of thecontrol pin 81. In fact, the angular displacement of the forks 78resulting from the displacement of the control pin 81 results in thecase of each associated pinion 69 in an equal angular displacementinasmuch as the fork 78 is coupled to said pinion 69 by means of the nut77. The rotation of said pinion 69 is then transmitted by means of theplanetary pinion 96 which is positionally fixed to the pinion 68 byreversing the direction of angular displacement. As a result, thedisplacements of the control pin 81 within the slot 85, that is to sayinside the reference circle, determine in the case of the center ofrotation of the vehicle corresponding displacements outside the basecircle between infinity and the limits of said circle as defined by theextremities of the corresponding diameter of the slot 85.

This mode of operation is therefore identical with the operation whichwas explained in connection with the first embodiment, the onlydifference being a mechanical variant in the method of keying thepivotal shafts and the pinions which control their angulardisplacements. However, the alternative form which is illustrated inFIG. also makes it possible to vary the position of the slot 85 or inother words, on the reference circle, to modify the, orientation of thediameter along which the transformed point of the center of rotationeffects a displacement.

ln point of fact, it has been noted that in the case of a position ofthe control pin 81 at one of the limits of its slot 85, thecorresponding orientation of the axle-pins 62 of the wheels is such thatsaid axle-pins are parallel to the associated forks 78. Under theseconditions, the rotary disc 86 in which is formed the slot 85 can becaused to pivot about its shaft 91 in particular by means of the pinion88 and driving pin 90 without modifying this orientation, that is to saywithout subjecting the drive pinions 68 and 69 to a relative movementwith respect to their pivotal shaft 64. To this end, the pinions 92,93and 94 are so designed that they retain a parallel relation between theaxle-pins 62 and the forks 78 during the rotation of the disc 86irrespective of the orientation of the slot 85. This means that, in thecase of a rotation of the slot about its axis through any angle a, theplanetary pinions 96 which are each associated with the pivotal shafts64 rotate about their own axes through an angle equal to 01/2. This isreadily apparent if reference is made to FIG. 6' in which the circle 100designates the reference circle, the straight line 1 J designatesthe'diameter of said circle corresponding to the slot 85 and Kdesignates the position of any one pivotal shaft 64; K1 represents inthe case of a limiting position of the fork-control pin the direction ofthe axis of the associated wheel. When the diameter 1] pivots about thecenter 0 of the circle through any angle a so as to come to l' J it isapparent that, in order that the wheel should retain its orientation, K]in move to KJ. ln point of fact, this makes it necessary for to be equalto 01/2, which is in fact realized on the circle 100.

Referring again to FIG. 5, it is seen that the rotation of the slot 85results in a rotational movement of the pinion 92 through the angle awhich corresponds to an angular displacement of the pinion 93 which isequal but of opposite direction and in an angular displacement in thesame direction but through a half-angle in the case of the pinion 94which is secured to the pivotal shaft 64. This movement of rotation ofthe pinion 94 is transmitted to the planetary pinion 96 which performs apivotal movement about the pinions 68 and 69 without thereby causing anyrelative motion of these latter. In consequence, the operation of theassembly as a whole is retained without any modification in the positionof said pinions. lt will naturally be understood that the demonstrationdescribed above and contemplated in the particular case in which thecontrol pin 81 is located at one end of its slot 85 could be repeated inthe same manner in any position of said control pin.

FIG. 7 illustrates another alternative construction of the inventionwhich is similar to the embodiment of H6. 1 but in which thetransmission of the angular displacements of the forks for producing theconvergence of the pivotal axes of the wheel towards the transformedpoint of the circle of rotation or towards the harmonic conjugatethereof relative to the reference circle is no longer obtained by meansof a mechanical coupling system of the pinion type but is carried out bymeans of a potentiometer control system. This arrangement according tothe invention is more especially, although not solely, applicable to thecase in which the forces to be developed in order to turn the wheelscannot be obtained by means of simple forks, the mechanical strength ofwhich might prove inadequate. The arrangement referred to also makes itpossible to coordinate the orientation of the wheels from a distance,the position of each pivotal shaft associated with any wheel beingcontrolled by means of an independent electric motor which is directlycoupled to said shaft. In this FlG., the frame 110 which is illustratedcomprises a plurality of wheels 111 (four in number in the example)which are assumed to be driving and steerable wheels and mounted onaxle-pins 112, said axle-pins being in turn supported by pivots 113about which the wheel orientation control is effected. The frame 110 isassociated with a coordination plate 114 which can be completelyseparate from said frame and placed in' particular at a distance fromthis latter, circular control potentiometers which are associated withthe wheels of the vehicle being mounted on said plate 114. Only two ofthese potentiometers 115 and 116 have been shown in the drawings for thesake of greater simplicity, it being understood that the plate 114 infact supports a number of potentiometers corresponding to the number ofwheels, each pivot 113 being additionally associated on the frame 110with a potentiometer for duplicating the control potentiometer of thecoordination plate. In this FlG., the potentiometers 115 and 116 thuscorrespond respectively to two potentiometers 117'and 118. mounted onthe shafts 119 and 120 of two motors 121 and 122 which are directlycoupled with the pivots 113 of the corresponding wheels 1 l 1.

The diagram of FIG. 8 which again shows side by side the frame 110 ofthe vehicle and the control'plate 114 with the control potentiometers115 and 116 on the one hand and 117 and 118 on the other hand serves toexplain the operation of the device in the embodiment 'underconsideration, this operation being naturally based on the same generalarrangements which were explained in connection with the alternativemechanical control systems described earlier. I

By definition, the axes of the pivots 113 of the vehicle wheels are allparallel and disposed at intervals in a circle which defines the basecircle of the vehicle. Similarly, the control potentiometers on theplate 114 are uniformly spaced in a circle which constitutes thereference circle as deduced from the base circle by means of anyperfectly defined geometrical transformation. The sliding contacts 123and 124 of the control potentiometers 115 and 116 are connected by forksor any like means 125 and126 to a control pin 127 which is displaceablealong a diameter128, 129 of the reference circle. Said potentiometersare supplied with a direct-current voltage having polarities which aresuitably distributed at the terminals of said potentiometers, thevoltage collected at the sliding contacts being returned to theassociated duplicating potentiometers, that is to say towards thepotentiometers 117 and 118 in the case considered. If saidpotentiometers are connnected in such a manner as to conform to thepolarities of the control potentiometers, it is apparent that thedisplacement of the control pin 127 on the plate 114 within the limitsof the diameter 128 and 129 carries out by means of followup control asimilar displacement of the point 130 towards which the sliding contacts131 and 132 of the duplicating potentiometers converge on the diameter133, 134 of the base circle in parallel relation to the sliding contacts123 and 124. In respect of a displacement of the center of rotationinside the base circle, its transformed point 127 inside the referencecircle is thus caused to correspond to said center of rotation in amanner which is exactly similar to that contemplated in the proceedingvariants.

Finally, P16. 9 shows the manner in which electric switching is carriedout in this case at the limits of the reference circle so as to causethe center of rotation within the base circle to correspond not to itstransformed point within the reference circle but to its harmonicconjugate with respect to said circle.

in order to pass beyond the limiting points of the reference circle, useis made of duplicating potentiometer 118 having two diametricallyopposite sliding contacts 132 and 132a. Only one of the two slidingcontacts will be employed, namely the particular contact which islocated within the useful zone of said potentiometer, that is to say atan angular distance of 90 on each side of the zero voltage point.

Under these conditions, the manner in which the center of rotationoversteps first the limiting point 133, then the limiting point 134 willnow be usefully considered. When the control pin 127 coincides with thelimiting point 128, the sliding contact 124 of the potentiometer 116produces action on the contact 135 which accordingly energizes the relay136. This relay then reverses the voltage at the terminal of thepotentiometer 116 opposite to the point 129, for example +12 V to -l2 V.In

consequence, when the control pin 127 again passes along the diameterl28-l29 but in the opposite direction, the sliding contact 132 of theduplicating potentiometer oversteps the limiting point which correspondsto the extremity 133 of the diameter of the base circle and continues totravel in the same direction while displacing the center of rotation 130outside the base circle and no longer inside this latter.

Similarly, when the center of rotation passes beyond the point 134, thecontrol pin 127 coincides with the point 129 and produces action on thecontact 137 which accordingly energizes a relay 138. This relay 138 hasthe effect on the one hand of causing the supply voltage at the terminalof the potentiometer 116 located opposite to the point 129 to changeover from 12 V to l2 V and on the other hand of replacing the slidingcontact 132 of the potentiometer 1118 by a sliding contact 132a which isdiametrically opposite to the same potentiometer 118. When the controlpin 127 moves again in the opposite direction, the sliding contact132-132a of the duplicating potentiometer oversteps the limiting pointwhich corresponds to the extremity 134 of the diameter of the basecircle. The geometrical transformation which is thus carried out permitsof continuous and unlimited displacement of the center of rotation.

It will be readily understood that the invention is not limited solelyto the examples herein described with reference to the accompanyingdrawings but extends to all alternative forms. In particular, in thecase of the embodiment last considered, it is possible to set thediameter of the reference circle on which the control pin is displacedin a number of different positions and especially in two perpendiculardirections. In this case, the duplicating potentiometers can beassociated alternately with two sets of control potentiometers which arerespectively located with respect to these directions. Moreover, it hasbeen assumed in all cases that the pivotal shafts of the wheels were allparallel to each other; it would also be possible to contemplate themore general case of nonparallel shafts which would in that case becoupled by means of universal joint transmission systems or the like tointermediate shafts which would have the function of maintaining thenecessary parallel relation.

We claim:

1. Method for controlling the steering of the wheels of a vehicle inwhich the pivot. axes of the wheels intersect a base plane at thevertices of a base polygon inscribed within a base circle, the baseplane being parallel to a plane passing through the axes of rotation ofthe wheels and corresponding to a reference circle in a reference planeby a geometrical transformation, the steps of continuously convergingthe rotational axes of the wheels towards a common point and center ofrotation of the vehicle lying on the axis of rotation of the vehicle,and maintaining the axis of rotation of the vehicle to intersect thebase plane at a base point, related selectively to a transformed pointin the reference circle related thereto by said geometricaltransformation and to the conjugate of the transformed point withreference to the reference circle.

2. Method in accordance with claim 1, wherein said transformed point isdisplaceable along a straight line in the reference plane.

3. Method in accordance with claim 2, wherein said straight line ispivotable about a point in said reference plane for continuously varyingthe position of the transformed point in the reference plane.

4. Apparatus for controlling the steering of the wheels of a vehicle inwhich the pivot axes of the wheels intersect a base plane at thevertices of a base polygon inscribed within a base circle, the baseplane being parallel to a plane passing through the axes of rotation ofthe wheels and corresponding to a reference circle in a reference planeby a geometrical transformation, comprising means for causing therotational axes of the wheels to continuously converge towards a commonpoint and center of rotation of the vehicle lying on the axis ofrotation of the vehicle, the axis of rotation of the vehicleintersecting the base plane at a base point related alternatively to atransformed point in the reference circle related thereto by saidgeometrical transformation or to the conjugate of the transfonned pointwith reference to said reference circle, said means including a firstset of bifurcated members pivotally 5 mounted at the vertices of areference polygon corresponding by said geometrical transformation tosaid base polygon, said members engaging a control pin, said pinintersecting said reference plane at said transformed point and beingmovable along a first linear guide slot in said reference plane.

5. Apparatus in accordance with claim 4, including a second set ofbifurcated members pivotally mounted at the vertices of said basepolygon, engaging a second control pin intersecting said base plane atsaid base point and movable along a second linear guide slot in saidbase plane. 7

6. Apparatus in accordance with claim 5, including a control plate, saidfirst and second guide slots being formed in said plate, first pinions,swivel pins for said first pinions extending parallel to the pivot axesof the wheels mounted on said control plate and positioned with theircenter at the vertices of said base polygon, said first set ofbifurcated members engaging said swivel pins and extending parallel tothe plane of said control plate, second pinions having the same diameteras said first pinions rigidly fixed to pivotal shafts for the wheels ofthe vehicle positioned with their centers at the vertices of saidreference polygon and connected with said first pinions, said second setof bifurcated members engaging said pivotal shafts, said referencecircle being deduced by translation of said base circle in the directionof a line joining said pivotal shafts to the axes of the associatedswivel pins and the amplitude of the translation being equal to thedistance between the centers of associated ones of said first and saidsecond pinions.

7. Apparatus in accordance with claim 6, wherein said reference plane isin the plane of said base plane and associated ones of said first andsaid second pinions are in meshing relation.

8. Apparatus in accordance with claim 6, wherein the said line isparallel to said first slot and said first slot coincides with saidsecond slot.

9. Apparatus in accordance with claim 6, said bifurcated members of saidfirst and said second sets being parallel and disposed, respectively, oneach side of said control plate.

10. Apparatus in accordance with claim 4, including a control plate,said first guide slot being formed in said plate, first and secondpinions carried by pivotal shafts for the vehicle wheels, said shaftsbeing positioned with their centers at the vertices of said referenceand said base polygons respectively and alternatively engageable withsaid pivotal shafts, said first set of bifurcated members being mountedon said first pinions, a planetary pinion coupling associated ones ofsaid first and said second pinions the diameter of said planetary piniondefining the amplitude of translation in the direction of said pivotalshafts, a set of third identical pinions coupled with said pivotalshafts and in meshing relation through bevel pinions with a fourthpinion, a shaft for said fourth pinion parallel to said pivotal shaftsand supporting said control plate, the diameter of said fourth pinionbeing equal to the diameter of said bevel pinions and to one-half thediameter of said third pinions.

11. Apparatus for controlling the steering of the wheels of a vehicle inwhich the pivot axes of the wheels intersect a base plane at thevertices of a base polygon inscribed within a base circle, the baseplane being parallel to a plane passing through the axes of rotation ofthe wheels and corresponding to a reference circle in a reference planeby a geometrical transformation, comprising means for causing therotational axes of the wheels to continuously converge towards a commonpoint and center of rotation of the vehicle lying on the axis ofrotation of the vehicle, the axis of rotation of the vehicleintersecting the base plane at a base point related alternatively to atransformed point in said reference circle related thereto by saidgeometrical transformation or to the conjugate of the transformed pointwith reference to said reference circle, said means including a controlplate, a set of circular electric potentiometers on said plate disposedon said reference circle at the vertices of a reference polygoncorresponding respectively to said base circle and said base polygon bya similitude', sliding contacts for said 'potentiometers, radiallyextending members carrying said contacts converging towards a commoncontrol pin, said pin being movable along a diameter of said referencecircle, pivotal shafts for the wheels, individual motors rotating saidshafts, duplicating potentiometers as- 4 sociated with saidpotcntiometers on said control plate, sliding contacts for saidduplicating potentiometers and circuit means supplying said motors as afunction of the positions of said

1. Method for controlling the steering of the wheels of a vehicle inwhich the pivot axes of the wheels intersect a base plane at thevertices of a base polygon inscribed within a base circle, the baseplane being parallel to a plane passing through the axes of rotation ofthe wheels and corresponding to a reference circle in a reference planeby a geometrical transformation, the steps of continuously convergingthe rotational axes of the wheels towards a common point and center ofrotation of the vehicle lying on the axis of rotation of the vehicle,and maintaining the axis of rotation of the vehicle to intersect thebase plane aT a base point, related selectively to a transformed pointin the reference circle related thereto by said geometricaltransformation and to the conjugate of the transformed point withreference to the reference circle.
 2. Method in accordance with claim 1,wherein said transformed point is displaceable along a straight line inthe reference plane.
 3. Method in accordance with claim 2, wherein saidstraight line is pivotable about a point in said reference plane forcontinuously varying the position of the transformed point in thereference plane.
 4. Apparatus for controlling the steering of the wheelsof a vehicle in which the pivot axes of the wheels intersect a baseplane at the vertices of a base polygon inscribed within a base circle,the base plane being parallel to a plane passing through the axes ofrotation of the wheels and corresponding to a reference circle in areference plane by a geometrical transformation, comprising means forcausing the rotational axes of the wheels to continuously convergetowards a common point and center of rotation of the vehicle lying onthe axis of rotation of the vehicle, the axis of rotation of the vehicleintersecting the base plane at a base point related alternatively to atransformed point in the reference circle related thereto by saidgeometrical transformation or to the conjugate of the transformed pointwith reference to said reference circle, said means including a firstset of bifurcated members pivotally mounted at the vertices of areference polygon corresponding by said geometrical transformation tosaid base polygon, said members engaging a control pin, said pinintersecting said reference plane at said transformed point and beingmovable along a first linear guide slot in said reference plane. 5.Apparatus in accordance with claim 4, including a second set ofbifurcated members pivotally mounted at the vertices of said basepolygon, engaging a second control pin intersecting said base plane atsaid base point and movable along a second linear guide slot in saidbase plane.
 6. Apparatus in accordance with claim 5, including a controlplate, said first and second guide slots being formed in said plate,first pinions, swivel pins for said first pinions extending parallel tothe pivot axes of the wheels mounted on said control plate andpositioned with their center at the vertices of said base polygon, saidfirst set of bifurcated members engaging said swivel pins and extendingparallel to the plane of said control plate, second pinions having thesame diameter as said first pinions rigidly fixed to pivotal shafts forthe wheels of the vehicle positioned with their centers at the verticesof said reference polygon and connected with said first pinions, saidsecond set of bifurcated members engaging said pivotal shafts, saidreference circle being deduced by translation of said base circle in thedirection of a line joining said pivotal shafts to the axes of theassociated swivel pins and the amplitude of the translation being equalto the distance between the centers of associated ones of said first andsaid second pinions.
 7. Apparatus in accordance with claim 6, whereinsaid reference plane is in the plane of said base plane and associatedones of said first and said second pinions are in meshing relation. 8.Apparatus in accordance with claim 6, wherein the said line is parallelto said first slot and said first slot coincides with said second slot.9. Apparatus in accordance with claim 6, said bifurcated members of saidfirst and said second sets being parallel and disposed, respectively, oneach side of said control plate.
 10. Apparatus in accordance with claim4, including a control plate, said first guide slot being formed in saidplate, first and second pinions carried by pivotal shafts for thevehicle wheels, said shafts being positioned with their centers at thevertices of said reference and said base polygons respectively andalternatively engageable with said pivotal shafts, said fiRst set ofbifurcated members being mounted on said first pinions, a planetarypinion coupling associated ones of said first and said second pinionsthe diameter of said planetary pinion defining the amplitude oftranslation in the direction of said pivotal shafts, a set of thirdidentical pinions coupled with said pivotal shafts and in meshingrelation through bevel pinions with a fourth pinion, a shaft for saidfourth pinion parallel to said pivotal shafts and supporting saidcontrol plate, the diameter of said fourth pinion being equal to thediameter of said bevel pinions and to one-half the diameter of saidthird pinions.
 11. Apparatus for controlling the steering of the wheelsof a vehicle in which the pivot axes of the wheels intersect a baseplane at the vertices of a base polygon inscribed within a base circle,the base plane being parallel to a plane passing through the axes ofrotation of the wheels and corresponding to a reference circle in areference plane by a geometrical transformation, comprising means forcausing the rotational axes of the wheels to continuously convergetowards a common point and center of rotation of the vehicle lying onthe axis of rotation of the vehicle, the axis of rotation of the vehicleintersecting the base plane at a base point related alternatively to atransformed point in said reference circle related thereto by saidgeometrical transformation or to the conjugate of the transformed pointwith reference to said reference circle, said means including a controlplate, a set of circular electric potentiometers on said plate disposedon said reference circle at the vertices of a reference polygoncorresponding respectively to said base circle and said base polygon bya similitude, sliding contacts for said potentiometers, radiallyextending members carrying said contacts converging towards a commoncontrol pin, said pin being movable along a diameter of said referencecircle, pivotal shafts for the wheels, individual motors rotating saidshafts, duplicating potentiometers associated with said potentiometerson said control plate, sliding contacts for said duplicatingpotentiometers and circuit means supplying said motors as a function ofthe positions of said last-named sliding contacts.
 12. Apparatus inaccordance with claim 11, including relays on said control plate at theextremities of the diameter of said reference circle along which saidcontrol pin is movable for reversing the directions of polarity of saidduplicating potentiometers and for providing alternative correspondencebetween said center of rotation and its transformed point and theconjugate of the transformed point relative to said reference circle.